This invention relates generally to a submersible probe adapted to continuously analyze the concentration of a gas such as oxygen dissolved in a liquid, and more particularly to a probe of this type having an improved measuring electrode structure.
In liquid wastes, the factor which determines whether biological changes are being brought about by aerobic or by anaerobic organisms is dissolved oxygen. Aerobic activity requires free oxygen and produces innocuous end products, whereas anaerobic activity can utilize chemically bonded oxygen such as sulfates to produce end products which are obnoxious. Because both types are ubiquitous in nature, it is vital in waste treatment that conditions conducive to aerobic activity be encouraged, for otherwise anaerobic organisms will take over.
Thus in aerobic treatment processes intended to purify sewage and industrial wastes, the present practice is to continuously measure the dissolved oxygen in order to monitor and maintain proper aerobic conditions. Since all aerobic treatment techniques depend upon the presence of dissolved oxygen, the continuous testing thereof is essential when regulating the rate of aeration not only to insure that the supply of oxygen is adequate to maintain aerobic conditions, but also to prevent excessive use of energy needed for aeration.
The need for dissolved oxygen measurement is by no means limited to sanitary engineering, for oxygen is a significant factor in iron and steel corrosion, such as in steam boilers. Thus in control systems for removing oxygen from boiler-feed waters, it is customary in the power industry to measure the dissolved oxygen concentration.
Dissolved oxygen probes of the electrochemical type are well known. Some of these probes exploit the magnitude of the depolarizing effect of oxygen on a special galvanic cell. Thus in U.S. Pat. Nos. 3,510,421 and 3,239,444 there are disclosed embodiments of electrochemical cells which are immersible in liquid for measuring the concentration of dissolved oxygen. In its simplest form, the cell is constituted by an anode or counter-electrode and a cathode or measuring electrode bridged by an electrolyte. The cell is adapted by means of a diffusion membrane covering the measuring electrode and permeable only to gases but impermeable to liquids to receive a sample of oxygen. Upon the entry of the sample, a chemical reaction occurs, modifying the electrical characteristics of the cell. Also of background interest is the 1976 patent to Poole, U.S. Pat. No. 3,948,746 and the prior art cited therein.